This proposal focuses on four aspects of current work concerning neurotensin (NT) and its co-stored variant, neuromedin N (NMN). Regulation of NT/NMN expression will be investigated in several in vivo (rat) systems associated with altered peptide levels. This will be done by characterizing and quantitating NT/NMN message, precursor and peptide through the course of increased or decreased production in order to determine whether altered gene transcription or precursor processing is involved. Precursor processing events will also be studied in whole tissues and in isolated canine N- cells, taking advantage of the recently determined cDNA sequence for NT/NMN precursor. Antibodies towards several regions of the precursor will be used to identify key intermediates and potentially active peptides. In addition, we will isolate, identify and pharmacologically characterize the large molecular forms of NMN which comprise most (>90%) of the total NMN in canine intestine. Preliminary work shows high affinity receptor(s) for NT/NMN in porcine brain which we pian to characterize and purify using affinity methods. Long term goals are to clone the receptor and identify its binding pocket. Lipid is the most potent stimulus for intestinal secretion of NT. Recent work in our laboratory indicates that surges in plasma levels of NT occur 1-3 hrs after eating and 8-12 hrs after eating. Studies are designed to investigate potential functions of NT at these times. Neutralizing antisera and peptide antagonists will be used to test the hypothesis that NT or NMN is responsible for the increased vascular permeability and lymph flow associated with fat digestion. Additional studies will ask whether NT participates in the liver glycogenolytic response seen 8-12 hrs after eating.